It is generally known in the art to power turbines with gases being expelled from combustion chambers. These gas powered turbines can produce power for many applications such as terrestrial power plants. In the gas powered turbine a fuel is combusted in an oxygen rich environment. The fuel may be any appropriate fuel such as a liquid or gas. Exemplary fuels include hydrocarbons (for example methane or kerosene) or hydrogen. Generally, these combustion systems may emit undesirable compounds such as nitrous oxide compounds (NOX) and carbon containing compounds. It is generally desirable to decrease various emissions as much as possible so that selected compounds may not enter the atmosphere. In particular, it has become desirable to reduce NOX emissions to a substantially low amount. Emissions of NOX are generally desired to be near zero, and are accepted to be near or at zero, if they are equal to or less than about one part per million volume of dry weight emissions.
A combustion chamber fuel, such as methane, is combusted in atmospheric air where temperatures generally exceed about 1427° C. (about 2600° F.). When temperatures are above 1427° C., the nitrogen and oxygen compounds, both present in atmospheric air, undergo chemical reactions which produce nitrous oxide compounds. The energy provided by the high temperatures allows the breakdown of dinitrogen and dioxygen, especially in the presence of other materials such as metals, to produce NOX compounds such as NO2 and NO.
It has been attempted to reduce NOX compounds by initially heating the air before it enters the combustion chambers to an auto-ignition temperature. If the air enters the combustion chamber at an auto-ignition temperature, then no flame is necessary to combust the fuel. Auto-ignition temperatures are usually lower than pilot flame temperatures or the temperatures inside recirculation flame holding zones. If no flame is required in the combustion chamber, the combustion chamber temperature is lower, at least locally, and decreases NOX emissions. One such method is to entrain the fuel in the air before it reaches the combustion chamber. This is done substantially continuously throughout operation of the combustor. The air or oxidizer must be heated with pre-burning to operate at all. This vitiated air, that is air which includes the fuel, is then ignited in a pre-burner to raise the temperature of the air before it reaches the main combustion chamber. This decreases NOX emissions substantially. Nevertheless, NOX emissions still exist due to the initial pre-burning. Therefore, it is desirable to decrease or eliminate this pre-burning, thereby substantially eliminating all NOX emissions.
Although the air is heated before entering the main combustion chamber, it may still be ignited in the combustion chamber to combust the remaining fuel. Therefore, an additional flame or arc is used to combust remaining fuel in the main combustion chamber. Again the flame or arc is generally always required to maintain combustion. This reduces the temperature of the igniter, but still increases the temperature of the combustion chamber. In addition, no fuel is added to the air as it enters the combustion chamber. Rather all the fuel has already been entrained in the air before it enters the combustion chamber to be combusted. This greatly reduces control over where combustion occurs and the temperature in the combustion chamber.
Other attempts to lower NOX emissions include placing catalysts in catalytic converters on the emission side of the turbines. This converts the NOX compounds into more desirable compounds such as dinitrogen and dioxygen. These emission side converters, however, are not one hundred percent efficient thereby still allowing NOX emissions to enter the atmosphere. The emission converters also use ammonia NH3, gas to cause the reduction of NOX to N2. Some of this ammonia is discharged into the atmosphere. Also, these converters are expensive and increase the complexity of the turbine and power production systems. Therefore, it is also desirable to eliminate the need for emission side catalytic converters.
Furthermore, it may be desirable to provide substantially simultaneous ignition of a plurality of combustors. This may reduce undesirable emissions, while increasing longevity of the system. For example, if only a limited number of a selected number of combustors are ignited at once and a combustion or shock wave is used to ignite the others, substantial back pressures and undesirable stresses may be exerted on the system. Therefore, igniting each of the combustors substantially simultaneously may decrease the stress placed on the system and increase the efficiency of the start up, thereby decreasing selected emissions.